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Loans And Allowance For Loan Losses (Summary Classification Of Held To Maturity Loan Portfolio) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Loans And Allowance For Loan Losses [Line Items]    
Total loans $ 11,469,238us-gaap_LoansAndLeasesReceivableGrossCarryingAmount $ 10,956,836us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Business [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 3,969,952us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember		 3,715,319us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
Real Estate - Construction And Land [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 403,507us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember		 406,197us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
Real Estate - Business [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 2,288,215us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember		 2,313,550us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
Real Estate - Personal [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 1,883,092us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_PersonalRealEstateLoanMember		 1,787,626us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_PersonalRealEstateLoanMember
Consumer [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 1,705,134us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoanMember		 1,512,716us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoanMember
Consumer Credit Card [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 782,370us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember		 796,228us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember
Overdrafts [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 6,095us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_OverdraftsMember		 4,611us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_OverdraftsMember
Personal Banking Portfolio Segment [Member] | Real Estate - Personal [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 1,883,092us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_PersonalRealEstateLoanMember		 1,787,626us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_PersonalRealEstateLoanMember
Personal Banking Portfolio Segment [Member] | Consumer [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 1,705,134us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoanMember		 1,512,716us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoanMember
Personal Banking Portfolio Segment [Member] | Revolving Home Equity [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 430,873us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_RevolvingCreditFacilityMember		 420,589us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_RevolvingCreditFacilityMember
Personal Banking Portfolio Segment [Member] | Consumer Credit Card [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans 782,370us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember		 796,228us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerCreditCardFinancingReceivableMember
Personal Banking Portfolio Segment [Member] | Overdrafts [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Total loans $ 6,095us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_OverdraftsMember		 $ 4,611us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_OverdraftsMember